There are a number of conventional processes for packaging integrated circuit (IC) dice. By way of example, many IC packages utilize a metallic leadframe that has been stamped or etched from a metal sheet to provide electrical interconnects to external devices. The die may be electrically connected to the leadframe by means of bonding wires, solder bumps or other suitable electrical connections. Often, the die and portions of the leadframe are encapsulated with a molding material to protect the delicate electrical components on the active side of the die while leaving selected portions of the leadframe exposed to facilitate electrical connections to external devices.
At various times, package designs have been proposed that utilize a metal foil as the electrical interconnect structure in place of the leadframe. Although a number of foil based designs have been developed, none have achieved widespread acceptance in the industry in part because foil based packaging processes tend to be more expensive than conventional leadframe packaging. Accordingly, there are continuing efforts to develop more efficient techniques that improve the cost competitiveness of foil based packaging.
When a metal foil is used to form the interconnects of an integrated circuit package, it is sometimes desirable to pre-plate one side (and only one side) of the foil with a thin metal layer. For example, in packages that utilize gold bonding wires to electrically connect a die to a copper foil, it may be desirable to silver plate the side of the foil that forms the wire bonding surface. This may be desirable because, as is well known in the art, gold does not adhere well to copper but does adhere reasonably well to silver plating. Thus, an intermediate silver layer may be used to help anchor the bonding wires more securely to the foil.
One way to silver plate selected portions of a foil would be to mask portions of the foil that are not to be plated with a dielectric while leaving portions of the foil that are to be plated exposed. The exposed portions of the foil may then be plated using conventional electroplating techniques. Although such a masking approach works well, more cost effective methods for pre-coating a single side of a metal foil are desirable. The present invention provides improved processes for plating foils suitable for use in semiconductor packaging.